(1) Field of the Invention
This invention pertains generally to fluid flow apparatus for aspirating and mixing two fluids, and is more particularly directed to apparatus of the type for obtaining a desired condition of the fluid mix with varying mix condition requirements, or varying conditions of the primary and secondary component fluids, or either of them. Still more particularly, the invention is directed to apparatus for supplying the ventilating air for an aircraft from a hot bleed source (the engine of the aircraft) and a cold air source with the cold air aspirated by the hot pressurized air, in the novel apparatus of the invention, and wherein the temperatures of the source airs may vary and the temperature selection of the ventilating air may vary.
(2) Description of the Prior Art
An approach to solutions for the problems associated with flow controls of the type is exemplified in U.S. Pat. No. 3,394,884 on an invention by T. J. Lord of a "System of Mixed Air Flows".
In that patent there is disclosed a spring biased sleeve valve which controls the relative amounts of primary and secondary air, supplied by a primary hot air pressurized source and secondary ambient air, respectively, that are admitted into a mixing duct for transport to the point of use.
The design of the patented valve of Lord is subject to several limitations and undesirable features: (1) the Lord valve uses a variable ejector to provide control of the ratio between primary and secondary airs; (2) the variable, single port ejector primary nozzle requires a relatively long downstream mixing duct for ambient air induction, characteristically a duct length of the order of about 50 times the effective valve diameter; (3) the Lord valve modulates ambient secondary air flow as well as primary bleed flow; (4) for a fixed bleed pressure, the patented device is a highly varying total mixed flow as the sleeve valve strokes, unless both the primary area vs. stroke and ambient secondary area vs. stroke characteristics are controlled; (5) for a given valve position, the Lord device will give different total flows as (primary) bleed pressure varies; (6) for most operating conditions, the Lord device drops full bleed pressure down to ambient across the variable ejector, generating a very high level of noise which is transmitted into the downstream duct.